Fiber-reinforced polymer composites are well known and widely used. Polymers of improved strength and increased stiffness can be obtained by the use of an appropriate reinforcing fiber. Probably the most widely used reinforcing fibers are glass, carbon and aramid (or "Kevlar" which is a registered trademark of the E. I. du Pont de Nemours & Co., Wilmington, Del.).
The base polymers used in making reinforced polymer composites such as those described above include a wide range of thermoplastics, such as polystyrene and copolymers thereof, polyamides, polycarbonates, polyetherimide, polyether etherketone (PEEK) and polyesters such as polybutylene terephthalate. These polymers are thermoplastics and are either amorphous or semi-crystalline. They may be called flexible chain polymers, since individual monomer units in the polymer chain are free to rotate with respect to each other so that the polymer chain may assume a random shape. By way of illustration, F. N. Cogswell, Intern. Polymer Processing, vol. 1, no. 4, pages 157-165 (1987) discloses carbon fiber-reinforced PEEK.
More recently developed are self-reinforced polymer composites comprising long, continuous, predominantly unidirectionally oriented fibers of a melt processable wholly aromatic polyester in a matrix of a thermoplastic flexible chain polymer. Such polymer composites are described for example in commonly assigned, U.S. Pat. No. 4,728,698 of Avraam Isayev et al., issued Mar. 1, 1988, and U.S. Pat. No. 4,835,047 of Avraam Isayev et al issued May 30, 1989. As described therein, the fibers of the wholly aromatic polyester, which may also be termed a thermotropic liquid crystal polymer (LCP), are long continuous fibers formed in situ by mixing the matrix of base polymer with the wholly aromatic polyester in a suitable mixing and extrusion apparatus, as for example, an extruder-static mixer setup, or a twin screw extruder.
Polymer composites specifically disclosed in U.S. Pat. No. 4,728,698 are polycarbonate/LCP composites containing from 2.5 to 50 weight percent of LCP, and polyetherimide/LCP composites containing from 5 to 30 percent by weight of LCP. Those described in U.S. Pat. No. 4,835,047 are composites of polyetherimide (PEI) and a wholly aromatic polyester or LCP, in which the LCP content varies from 40 to 95 percent by weight. These composites of PEI and an LCP are also described in A. I. Isayev and S. Swaminathan, "Thermoplastic Fiber-Reinforced Composites Based on Liquid Crystalline Polymers," Proceedings of the Third Annual Conference on Advanced Composites, pages 259-267, 15-17 September 1987, Detroit, Mich., published by ASM International.
U.S. Pat. No. 4,650,836 discloses a method for rendering melt processable a liquid crystal polymer (LCP) not otherwise readily processable, in which said LCP is blended with a second, low molecular weight liquid crystal diester. The low molecular weight diester may be transesterified into the polyester to produce a long chain having desirable final liquid crystal polymer properties.
M. P. De Meuse and M. Jaffe, Polymer Preprints, vol. 30, no. II, September 1989, pp 540-541, disclose LCP/LCP blends which are miscible in both the melt and solid states.
Neither U.S. Pat. No. 4,650,836 nor the above-cited Polymer Preprints article discloses the physical or mechanical properties of the respective blends.